A similar study of weight-lifting would conclude that it weakens you: after all, doing some squats leads to fatigue. Frequently an activity that causes effect X in the short term leads to its opposite when repeated over long periods; see drug habituation, the effects of physical exercise, the effects of intellectual efforts, etc. This study tells us that self-control might be a bit like a muscle, in that its use acut…
The chronic adaptation, in other words, is habit. The process of intentionally breaking old habits and establishing new ones seems to always be particularly taxing, but maintaining an established habit, regardless of what it is, is easy. (Ignoring external factors, of course.)
With that in mind, it would be good advice to conserve the limited resource, or at least acknowledge it's variable availability and adjust your expectations of your own abilities in accordance. I'm certain there are many among the ambitious folk of HN who have taken on too many new and exciting challenges at once only to find that they turn into new and exciting chores that we can't even force ourselves to do, instead turning to the things that don't require self-control instead.
We call that procrastination and treat it like a challenge to overcome, too, but if it's a symptom of depleted self-control (and not a weak self-control "muscle"), then we'd be better served by being miserly about how we spend it than by taxing it unnecessarily. In that sense, there is a meta-adaptation in how you consciously manage your attention.